Just a quick writeup on a flight I attempted on March 30th back home from Belgrade to Stuttgart. It was during the peak of the terrible cyclone Niklas in Germany that killed several people. I had worked out a good plan and then ruined it all.
The weather in Stuttgart appeared OK to me, a very strong wind (20-30kt) but not far off the runway orientation and rather constant. With plenty of endurance and better weather not far away as well as high altitude capability, I set off on the trip. There was a lot of IMC expected but freezing level was well above the ground and so was the ceiling which gave me enough ways out (ca ISA-2 in Austria/Germany). An easterly routing avoiding the Alps made gave additional safety. The air masses were cold and there was a possibility of cold weather thunderstorms.
The goal was to climb up high rather quickly and then stay on top with a good view of the weather situation. There were plenty of holes in several directions which gave ma a good feeling. FL190-FL200 was above the weather. Shortly after takeoff, just when reaching high altitude, my Mountain High O2D2 died — with the valve shut. This is a very annoying failure mode and I am still very unhappy. The only comment I got from the manufacturer was “you should send it in every 2 years for service”. Yeah, that costs ca. 300 € because they insist on sending it via UPS/Fedex and the like. So I had to switch to the mask and the builtin system which means the oxygen flow rate was very high (this played a role lateron).
I worked a lot with satellite weather using my Thuraya phone and my GSM phone. I use a collection of radar images and other stuff that I get from various internet sources, all private so without the issue of having to obtain a redistribution license. In this case you can see how I match a radar image of Hungary against my map:
For some of the maps, I built a little geo-refeferencing and mini moving map into the browser app which makes it much easier to follow. That one also has a mini airspace database builtin to the local web page (the page is completely stored in the browser and uses the builtin SQlite support of modern browsers, only the images get transferred).
So I realized I can stay on top of this weather and I was fairly confident I could find a way down at my destination and make a landing. Maybe not at my airfield but for sure at the big airport which would bring me home and get me another nice flight on one of the next days to bring the aircraft home. I was skimming just above the stuff in FL190 (with FL200 easily reachable and up to FL240 if I really have to, safe but outside the official aircraft limitations). What should happen?
As I got closer to the heart of the cyclone, the wind got stronger and stronger and I got slower and slower. Here you can see me doing 166KTAS of which only 80KTAS bring me closer to my destination — a whopping 90kt of wind pushing me back!
Flying like this can be frustrating. I hate headwinds and a wind like this, I’ve never seen. I was getting very annoyed and started looking for ways to improve the situation. In addition to that I saw my oxygen level go down rapidly as I was consuming a lot of it with the face mask in FL190. Assuming a non linear degradation of the bottle (i.e. acceleration) and my low ground speed, I concluded that I might get low on oxygen with this ground speed and that this might significantly reduce my options later.
Then I came to the area of Linz LOWL where the weather looked marvellous compared to all the other places around.
I asked ATC what the lowest IFR level would be for my continued trip to Germany and they said FL060. At ISA-2 that would be 15 – 2 * 6 = +3°C. In additional the wind would be much less there. The data from the satphone showed no thunderstorms down there and I had the feeling it might actually be VMC and if not, I would cancel IFR and continue probably the bumpiest ride in my career VFR but what the heck. Plenty of options.
So I asked for a descent from FL190 to FL060, hoping to complete it within the Linz beautiful weather area and without icing. Well, that didn’t work out exactly, I entered IMC at FL080 and continued a very fast descent. I immediately picked up ice and thought let’s go to FL060 then it will be over. How wrong I was! At FL060 it really started, I got into what I would classify as severe icing, it was growing in centimeters every few seconds, there were loud noises as the ice formed everywhere. Never seen anything like that, it was clear that I wouldn’t make it even for a minute in these conditions. Not a lot of pictures from that phase of the flight, I was at 150% of my mental capacity…
By the time I was already with Munich ATC but still in Austria. I immediately performed a 180 to the left (I always set my heading bug to the best way out before I enter dubious weather) and descended further (I had the MSA displayed and a good visual image of it, it was close to the mountains but my turn was into flat terrain).
Once I was out of the clouds and saw that the aircraft was still flying, I told ATC I had to perform a 180 due to severe icing and the only response was “Roger, contact Linz approach on xxxx”. They had already seen what I was doing and immediately understood my situation.
Landing in Linz was the best option cause I really needed a beer at this point. Linz approach said “I suggest you make a high speed visual approach as a CB is moving in right now”. I wanted to land and not wait for the CB to pass so I dove down while chunks of ice fell of the aircraft (nobody will ever figure out who killed those hikers on the ground with a hole in their head) and landed right before the thunderstorm. This is what it looked like after arrival.
The cyclone intensified in the coming day and I was stuck in Linz for two days. During the whole time, the train service in Austria and Germany was down and even cars were not driving. I’m lucky that my job only requires a good internet connection…
I basically made one mistake: annoyed by the headwind and in fear of depleted oxygen, I thought it would be better to fly low. The very small blue sky area of Linz further convinced me that this would be the right strategy. I don’t think I did anything foolish or dangerous, as I’ve followed the golden rule: have a way out. I knew the cloud could contain ice which is why I had a plan to get out and as a last resort I knew I could descent below the airway but above terrain and melt everything off. Had the Mountain High not failed, I would have made it on top of the weather to my destination where — as the sat weather confirmed — the situation was good enough for a safe descent.
Holy crap! I bet that beer tasted well!
Could you tell us a bit more about that Ice encounter? How cold was it actually at FL060 in the cloud(compared to your initial estimate)? Was there precip as well (and shown on sat radar) or just very ‘moist’ clouds in worst temp range (0 to -5)? When did ice finally start to melt, once you went back into clear and descended or once they actually let you further down for approach whilst still being IMC?
Very insightful about the quirks of weather. Your reasoning and logic behind your actions seem very straightforward and guess we all could easily have ended up in same situation.
I’ve got a MH o2d2 myself, never heard about that servicing…
Still, well done.
IME, the famous “2 degrees per 1000 feet rule” does not work at all in practice, in both directions. So we shouldn’t get too
mathematical about freezing levels. As Peter always says, the difference between “in cloud” and “outside cloud” can be worth 4 degrees alone.
Hoping for positive temps, in very instable atmosphere, on a 30th of March, in IMC, in Germany, is, err, optimistic.
As Peter always says, the difference between “in cloud” and “outside cloud” can be worth 4 degrees alone.
Much more than that on some occasions. In clear air though, the 2°/1000ft gradient is more or less correct.
Before flying into clouds, I always look at the outside air temperature indicator (because in our aircraft, the ignition is supposed to be turned on whenever there is visible moisture below +10°C) and have seen temperature drops in excess of 10 degrees. And also ice formation well above 0 degrees OAT.
Hi Achim, thanks for sharing.
I’ve got two O2D2 regulators to avoid a single point of failure.
One unit has quirks every now and then. For example the Delayed mode (D5, D10) is not working reliably and sometimes it gives false warnings that the user is not breathing.
The ISA lap rate can’t be used reliably to calculate where the freezing level will be.
I’ve had a situation during descent in IMC where it was 0°C for over 4000ft.
The 180 turn was a good decision and an example where you might be death if you had wait for approval from ATC…
That’s a scary ice encounter! The fastest I have had was about 3cm in 5 minutes and that was fast.
I too have two O2D2 regs, partly to supply up to four people and partly to give redundancy when flying with two. Yes, they do fail shut even though this was denied on various forums in the past. They also shut when the batteries run out. So I test the battery voltage from time to time and replace them before they might run out. I do wonder if they have had QA issues recently – based on what I have heard from other pilots.
The lapse rate of 2K/1000ft is probably about right for convective weather i.e. where you get lumps of the white fluffy stuff but only below the layer. In stratus conditions the lapse rate can be anything, is likely to be inverted at time, and as stated above will prob99 drop a few degrees the instant you enter cloud so if e.g. flying just above at +2C and you descend you will get assured icing especially in the tops which are the wettest.
Now I can understand what the term “icing encounter” actually means. Thanks for clarifying that… 
And … Good job in getting out of it!
Scary! You don’t think the icing could have made the airplane fall out of the sky? Happened more than once, so I don’t really understand why you think it was safe. I think it wasn’t completely safe but you did a good job!
I never understood why temperature in convective cloud is lower than outside – isn’t it supposedly the warmer air in the cloud compared to the surroundings that creates the convection?
I have made the same observation though … I fly in FL120 with +3 degrees and when I enter the cloud the temperature sometimes rapidly falls to -2 or -3 degrees.
